Cross-sectional imaging modalities such as CT and MR are increasingly capable of providing truly three-dimensional (3D) images. At present, however, diagnosis is mostly limited to examining individual cross-sectional images. We have entered into a collaboration with Silicon Graphics, Inc. and Vital Images, Inc. to develop and validate Perspective Volume Rendering (PVR), a new method for true 3D viewing of CT and MR patient examinations. Methods and Results PVR allows the user to simulate what a camera would see if placed anywhere exterior to or inside the volume of acquired images. In addition to control of the lighting and the camera position, orientation, and field of view, it is possible to selectively render structures invisible, opaque, or any where in between. This gives the camera variable "x-ray vision," so to speak, and permits optimal viewing of structures important to diagnosis and treatment planning. We have applied this technique to visualize, from within, the airways in the lungs, the major blood vessels, the colon, and joint spaces within the shoulder and knee. Note that the technique is not limited to exploration of hollow structures; i.e., soft tissues may be examined from within using the same computer hardware and software. Discussion PVR of CT and MR data provide virtual endoscopic views may be useful for diagnostic and treatment planning purposes. PVR may be used as a preliminary examination prior to actual endoscopy in order to screen out patients who are unlikely to benefit from the procedure. It also may be useful to monitor patients who have been treated for known diseases. PVR is a promising new technique for visualization of cross-sectional imaging data. Results of using PVR are likely to include substantial cost savings and reductions in morbidity from more invasive procedures.